Wearable dry electrodes are needed for long-term biopotential recordings but are limited by their imperfect compliance with the skin, especially during body movements and sweat secretions, resulting in high interfacial impedance and motion artifacts. Herein, we report an intrinsically conductive polymer dry electrode with excellent self-adhesiveness, stretchability, and conductivity. It shows much lower skin-contact impedance and noise in static and dynamic measurement than the current dry electrodes and standard gel electrodes, enabling to acquire high-quality electrocardiogram (ECG), electromyogram (EMG) and electroencephalogram (EEG) signals in various conditions such as dry and wet skin and during body movement. Hence, this dry electrode can be used for long-term healthcare monitoring in complex daily conditions. We further investigated the capabilities of this electrode in a clinical setting and realized its ability to detect the arrhythmia features of atrial fibrillation accurately, and quantify muscle activity during deep tendon reflex testing and contraction against resistance. Reported wearable dry electrodes have limited long-term use due to their imperfect skin compliance and high motion artifacts. Here, the authors report an intrinsically conductive, stretchable polymer dry electrode with excellent self-adhesiveness for long-term high-quality biopotential detection.

/pdf/fully-organic-compliant-dry-electrodes-self-adhesive-to-skin-iofhxwygxu.pdf

Fully organic compliant dry electrodes self-adhesive to skin for long-term motion-robust epidermal biopotential monitoring

Transparent and stretchable energy storage devices have attracted significant interest due to their potential to be applied to biocompatible and wearable electronics. Supercapacitors that use the reversible faradaic redox reaction of conducting polymer have a higher specific capacitance as compared with electrical double-layer capacitors. Typically, the conducting polymer electrode is fabricated through direct electropolymerization on the current collector. However, no research have been conducted on metal nanowires as current collectors for the direct electropolymerization, even though the metal nanowire network structure has proven to be superior as a transparent, flexible, and stretchable electrode platform because the conducting polymer's redox potential for polymerization is higher than that of widely studied metal nanowires such as silver and copper. In this study, we demonstrated a highly transparent and stretchable supercapacitor by developing Ag/Au/Polypyrrole core-shell nanowire networks as electrode by coating the surface of Ag NWs with a thin layer of gold, which provide higher redox potential than the electropolymerizable monomer. The Ag/Au/Polypyrrole core-shell nanowire networks demonstrated superior mechanical stability under various mechanical bending and stretching. In addition, proposed supercapacitors showed fine optical transmittance together with fivefold improved areal capacitance compared to pristine Ag/Au core-shell nanowire mesh-based supercapacitors.

Ag/Au/Polypyrrole Core-shell Nanowire Network for Transparent, Stretchable and Flexible Supercapacitor in Wearable Energy Devices.

Naturally derived materials with hierarchical organization are attractive candidates for high-performance and functional bionanocomposites because of their renewability, biocompatibility, biodegradability, flexibility, and the availability of multiple reactive sites for introducing novel functionalities. Complementary to these inherent properties, the synergistic combination of biological and synthetic components facilitated by strong interfacial interactions, can substantially enhance the structural performance and facilitate added functionalities of these bio-enabled nanocomposites. In this review, we discuss the current progress of naturally-derived bionanocomposites that has advanced our understanding of the biological/synthetic interfaces. In these bionanocomposites, various novel synthetic nanomaterials (e.g., graphene, carbon nanotube, mineral nanoparticles and metallic nanoparticles) are efficiently integrated with biological components to achieve novel properties such as superior electrical and thermal conductivity, controlled gas barrier properties, complex actuation, and unique optical properties. Two popular biocomponents, nanocellulose and silk, are mainly discussed in this review as representatives of classes of polysaccharides and polypeptides with some other biopolymers briefly discussed as well. The structures and morphologies, processing strategies, tailored functionalities and emerging applications of these bionanocomposites are analyzed and summarized. Finally, we present an outlook on the current trends in providing structural and interfacial enhancement as well as emerging applications which will employ new optical, sensing, structural, and actuating functionalities and properties.

Naturally-derived biopolymer nanocomposites: Interfacial design, properties and emerging applications

Inexpensive and easy-to-use diagnostic tools for fast health screening are imperative, especially in the developing world, where portability and affordability are a necessity. Accurate monitoring of metabolite levels can provide useful information regarding key metabolic activities of the body and detect the concomitant irregularities such as in the case of diabetes, a worldwide chronic disease. Today, the majority of daily glucose monitoring tools rely on piercing the skin to draw blood. The pain and discomfort associated with finger pricking have created a global need to develop non-invasive, portable glucose assays. In this work, we develop a disposable analytical device which can measure physiologically relevant glucose concentrations in human saliva based on enzymatic electrochemical detection. We use inkjet-printing technology for the rapid and low-cost deposition of all the components of this glucose sensor, from the electronics to the biorecognition elements, on commercially available paper substrates. The only electronic component of the sensor is the conducting polymer poly(3,4 ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS), while the biorecognition element comprises of the enzyme glucose oxidase coupled with an electron mediator. We demonstrate that one month after its fabrication and storage in air-free environment, the sensor maintains its function with only minor performance loss. This fully printed, all-polymer biosensor with its ease of fabrication, accuracy, sensitivity and compatibility with easy-to-obtain biofluids such as saliva aids in the development of next generation low-cost, non-invasive, eco-friendly, and disposable diagnostic tools. Saliva based glucose test can now be made easily and cheaply with inkjet-printed paper sensors enabled by enzyme glucose oxidase. Most present technologies rely on blood tests to monitor glucose concentration. To tackle this problem, a collaborative international team led by Prof Sahika Inal from King Abdullah University of Science and Technology, Saudi Arabia designs disposable glucose sensors based on saliva testing. They construct the analytical device by ink-jet printing cheap conducting polymer, an enzyme containing biological film and an encapsulation layer on paper substrates to measure glucose concentrations in human saliva. The devices stay active for more than a month in air-free storage conditions with minor performance losses. The high versatility and adaptability of the material system enable the possibilities to design affordable and expandable enzyme testing based diagnostic platforms.

/pdf/a-fully-inkjet-printed-disposable-glucose-sensor-on-paper-1mcrby7d8u.pdf

A fully inkjet-printed disposable glucose sensor on paper

Electrically interfacing the skin for monitoring personal health condition is the basis of skin-contact electrophysiology. In the clinical practice the use of stiff and bulky pregelled or dry electrodes, in contrast to the soft body tissues, imposes severe restrictions to user comfort and mobility while limiting clinical applications. Here, in this work dry, unperceivable temporary tattoo electrodes are presented. Customized single or multielectrode arrays are readily fabricated by inkjet printing of conducting polymer onto commercial decal transfer paper, which allows for easy transfer on the user's skin. Conformal adhesion to the skin is provided thanks to their ultralow thickness (<1 µm). Tattoo electrode-skin contact impedance is characterized on short- (1 h) and long-term (48 h) and compared with standard pregelled and dry electrodes. The viability in electrophysiology is validated by surface electromyography and electrocardiography recordings on various locations on limbs and face. A novel concept of tattoo as perforable skin-contact electrode, through which hairs can grow, is demonstrated, thus permitting to envision very long-term recordings on areas with high hair density. The proposed materials and patterning strategy make this technology amenable for large-scale production of low-cost sensing devices.

https://www.onlinelibrary.wiley.com/doi/epdf/10.1002/advs.201700771

Ultraconformable Temporary Tattoo Electrodes for Electrophysiology.

Conductive tattoo nanosheets are fabricated on top of decal transfer paper and transferred on target surfaces as temporary transfer tattoos. Circuits are patterned with ink-jet printing. Tattoo nanosheets are envisioned as unperceivable human-device interfaces because of conformal adhesion to complex surfaces including skin. They are tested as dry electrodes for surface electromyography (sEMG), which permits the control of a robotic hand.

Tattoo conductive polymer nanosheets for skin-contact applications.

Multiwalled carbon nanotubes (MWCNTs) were added to polyacrylamide (PAM) hydrogels in different proportions to tune their electrical and mechanical properties. The choice of MWCNTs as a reinforcement is justified by the fact that these are highly conducting, fairly stable and flexible particles. A series of MWCNT/PAM hydrogels were prepared by freezing method. The characteristic absorption peaks at 1480 and 1213 cm−1 in the FTIR spectra reveal that MWCNTs are embedded in the PAM hydrogels. Powder x-ray diffractograms and thermogravimetric analysis (TGA) images show that the MWCNT/PAM hydrogels are crystalline, more thermally stable and have a higher electrical conductivity than a traditional PAM hydrogel. Scanning electron micrographs reveal about reduced pore size, homogeneous and denser texture. The swelling properties of all these hybrid hydrogels were found to be better than those of the parent PAM hydrogel. The Li–Tanaka equation was employed to produce the swelling parameters. The diffusion coeffici...

Effect of Multiwalled Carbon Nanotubes on the Conductivity and Swelling Properties of Porous Polyacrylamide Hydrogels

The chiroptical properties of optically active polyaniline PANI(+)-HCSA emeraldine salt products in dimethylformamide (DMF) depend strongly on stereochemistry and steric crowding due to the presence of different moieties on the amino acids. Amino acids including L-arginine, L-proline, L-leucine, L-isoleucine, L-phenylalanine and L-lysine hydrochloride were used as precursors in emeraldine base/DMF solutions prior to acid doping with (S)-(+)-10-camphorsulfonic acid. Characterization of these materials was carried out using CD, UV-Vis and FTIR spectroscopic techniques. Our results indicate that the optical activity can be maintained for longer times in the solid and solution phases owing to the interactions and stabilization of polyaniline by hydrogen bond formation between the amino-acid molecules and the amine (NH) and imine (−N=) sites on the emeraldine base form, while preserving the stereo-selectivity of the polymer chain. This paper addresses the factors responsible for influencing the chiroptical properties in helical conducting polyaniline and the chiral discrimination of different amino acids. The main factors affecting the chirality and stability of PANI(+)-HCSA are moiety present, concentration, stereochemistry, chain length of the amino acids, time period for the doping, hydrogen bonding and so on. The corresponding CD spectra exhibited no measurable optical activity and consistent with complete de-doping of ES to EB. Further, on doping the solution, we have got the precipitate, which showed a remarkable optical activity. The CD spectra shows retention of the optical activity in solid phase obtained after de-doping of the solution.

/pdf/investigation-of-the-chiroptical-behavior-of-optically-27cc1duf47.pdf

Investigation of the chiroptical behavior of optically active polyaniline synthesized from naturally occurring amino acids

Conformable Electronics: Tattoo Conductive Polymer Nanosheets for Skin‐Contact Applications (Adv. Healthcare Mater. 7/2015)

The saturated solutions of chiral amino acids as soft template have been shown to function as a platform for induction of optical activity through free radical polymerization reaction. The conductivity of optically active polyaniline changes with the variation in acidity of reaction medium and morphology of the material. Ultraviolet-visible and circular dichroism spectra along with scanning electron microscopy and transmission electron microscopy micrographs evaluate discrete morphologies of polymers at different pH with phase segregation between unprotonated and fully protonated domains. Four probe method shows that the branched structure caused by the presence of phenazine units in polymer chain stabilizes different charge states in polymer with higher conductivity having higher dissymmetric g-factor. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Role of saturated solutions of chiral amino acids in synthesis and phase segregation within optically active polyaniline

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